#include<iostream>
using namespace std;

extern double warming;

void update(double add)
{
	extern double warming;//you can ignore this,it's permitted but not necessary.
	warming += add;
	cout << "update:warming increased by " << add << " and now global warming:" << warming << endl;
}

void local()
{
	double warming = 0.8;
	cout << "local warming:" << warming << endl;
	cout << "but global warming:" << ::warming << endl;
}
